1. Field of the Invention
This invention relates to ECL drivers implemented in CMOS, and more particularly to a PECL driver with programmable switching of current for implementing any voltage swing with standard or with non-standard termination.
2. Description of the Related Art
Today's computer networks handle an ever-increasing amount of data. Fast Ethernet transmits and receives packets at 100 Mbps, and other technologies such as asynchronous transfer mode (ATM) also require high data rates.
The highest-speed applications have traditionally used current-switching technologies such as bipolar NPN transistors arranged as emitter-coupled logic (ECL) gates and drivers. Bipolar NPN transistors have been added to complementary metal-oxide-semiconductor (CMOS) processes to support ECL. These CMOS processes with NPN transistors are known as BiCMOS. Unfortunately, such BiCMOS processes are expensive compared to standard CMOS.
CMOS operates with a 5-volt or 3-volt power supply and ground, but ECL traditionally operates with a negative power supply. Thus standard ECL voltage levels are not compatible with CMOS. A positive-voltage-shifted ECL known as pseudo-ECL (PECL) has been used for CMOS chips using ECL-type current drivers. See for example U.S. Pat. Nos. 5,495,184 and 5,089,723 which use CMOS transistors as current drivers for pseudo-ECL levels.